Optical refraction testing instrument



FIG. 1 is a perspective view of an optical refraction testinginstrument, showing my new design.

FIG. 2 is a front elevational view thereof.

FIG. 3 is a top plan view thereof.

FIG. 4 is a side elevational view as taken from the left hand side ofFIG. 2.

FIG. 5 is a bottom plan view thereof.

FIG. 6 is a rear elevational view thereof.

The ornamental design for an optical refraction testing instrument,substantially as shown.